Field of the Invention
The present disclosure relates to an organic light emitting diode display having a quantum dot. Particularly, the present disclosure relates to an organic light emitting diode display having a source energy layer which generates a high energy relating to the ultra violet wavelength range and has high light absorbing ability, and a quantum dot which receives the high energy from the source energy layer and generating lights having the visible light wavelength.
Discussion of the Related Art
Nowadays, various flat panel display devices are developed for overcoming many drawbacks of the cathode ray tube such as heavy weight and bulk volume. The flat panel display devices include a liquid crystal display device (or LCD device), a field emission display (or FED), a plasma display panel (or PDP) and an electroluminescence device (or EL). Specifically, the low temperature poly silicon is used for the active layer of the thin film transistor to get better quality of the flat panel displays.
The electroluminescence display device is categorized into an inorganic light emitting diode display device and an organic light emitting diode display device according to the luminescence material. As a self-emitting display device, the electroluminescence display device has merits in that the response speed is very fast, the brightness is very high and the view angle is large. The organic light emitting diode display has better energy efficiency and lower current leakage and is easier to represent the gray/color scale by current control.
FIG. 1 is a diagram illustrating the structure of the organic light emitting diode according to the related art. As shown in FIG. 1, the organic light emitting diode comprises an organic light emitting material layer and a cathode and the anode which are facing each other with an organic light emitting material layer therebetween. The organic light emitting material layer comprises a hole injection layer HIL, a hole transport layer HTL, an emission layer EML, an electron transport layer ETL and an electron injection layer EIL. The organic light emitting diode radiates the lights due to the energy from the exciton formed at the excitation state in which the hole and the electron are recombined at the emission layer EML.
The organic light emitting diode radiates the lights due to the energy from the exciton formed at the excitation state in which the hole from the anode and the electron from the cathode are recombined at the emission layer EML. The organic light emitting diode display can represent video data by controlling the amount (or ‘brightness’) of the light generated and radiated from the emission layer ELM of the organic light emitting diode as shown in FIG. 1.
The organic light emitting diode display (or OLED) using the organic light emitting diode can be categorized into a passive matrix type organic light emitting diode display (or PMOLED) and an active matrix type organic light emitting diode display (or AMOLED).
The active matrix type organic light emitting diode display (or AMOLED) shows the video data by controlling the current applying to the organic light emitting diode using the thin film transistor (or TFT).
FIG. 2 is the exemplary circuit diagram illustrating the structure of one pixel in the active matrix organic light emitting diode display (or AMOLED) according to the related art. FIG. 3 is a plane view illustrating the structure of the organic light emitting diode display using the thin film transistor according to the related art. FIG. 4 is a cross sectional view along the cutting line I-I′ in FIG. 3 for illustrating the structure of the bottom emission type organic light emitting diode display according to the related art. FIG. 5 is a cross sectional view along the cutting line I-I′ in FIG. 3 for illustrating the structure of the top emission type organic light emitting diode display according to the related art. As the differences between the bottom emission type and the top emission type are not shown in plane view, FIG. 3 is commonly used for these two emission types.
Referring to FIGS. 2 and 3, the active matrix organic light emitting diode display comprises a switching thin film transistor ST, a driving thin film transistor DT connected to the switching thin film transistor ST, and an organic light emitting diode OLED connected to the driving thin film transistor DT. By a scan line SL, a data line DL and a driving current line VDD disposed on a substrate SUB, a pixel area is defined. The organic light emitting diode OLED is formed in one pixel area and defines a light emitting area within the pixel area.
The switching thin film transistor ST is formed where the scan line SL and the data line DL are crossing. The switching thin film transistor ST acts for selecting the pixel which is connected to the switching thin film transistor ST. The switching thin film transistor ST includes a gate electrode SG branching from the gate line GL, a semiconductor channel layer SA overlapping with the gate electrode SG, a source electrode SS and a drain electrode SD. The driving thin film transistor DT acts for driving an anode electrode ANO of the organic light emitting diode OD disposed at the pixel selected by the switching thin film transistor ST.
The driving thin film transistor DT includes a gate electrode DG connected to the drain electrode SD of the switching thin film transistor ST, a semiconductor channel layer DA, a source electrode DS connected to the driving current line VDD, and a drain electrode DD. The drain electrode DD of the driving thin film transistor DT is connected to the anode electrode ANO of the organic light emitting diode OLE. Between the anode electrode ANO and the cathode electrode CAT, the organic light emitting layer OL is disposed. The cathode electrode CAT is connected to the base voltage VSS. Between the gate electrode DG of the driving thin film transistor DT and the driving current line VDD or between the gate electrode DG of the driving thin film transistor DT and the drain electrode DD of the driving thin film transistor DT, a storage capacitance Cst is formed.
Referring to FIG. 4, the bottom emission type organic light emitting diode display according to the related art will be explained in detail. On the substrate SUB, the gate electrodes SG and DG of the switching thin film transistor ST and the driving thin film transistor DT, respectively are formed. On the gate electrodes SG and DG, the gate insulator GI is deposited. On the gate insulator GI overlapping with the gate electrodes SG and DG, the semiconductor layers SA and DA are formed, respectively. On the semiconductor layer SA and DA, the source electrode SS and DS and the drain electrode SD and DD facing and separating from each other are formed. The drain electrode SD of the switching thin film transistor ST is connected to the gate electrode DG of the driving thin film transistor DT via the contact hole penetrating the gate insulator GI. The passivation layer PAS is deposited on the substrate SUB having the switching thin film transistor ST and the driving thin film transistor DT.
The upper surface of the substrate having these thin film transistors ST and DT is not in even and/or smooth conditions, but in uneven and/or rugged conditions having many steps. In order that the organic light emitting diode display has good luminescent quality over the whole display area, the organic light emitting layer OL should be formed on an even or smooth surface. So, to make the upper surface in planar and even conditions, the over coat layer OC (or ‘planar layer’) is deposited on the whole surface of the substrate OC.
Then, on the over coat layer OC, the anode electrode ANO of the organic light emitting diode OLE is formed. Here, the anode electrode ANO is connected to the drain electrode DD of the driving thin film transistor DT through the contact hole penetrating the over coat layer OC and the passivation layer PAS.
On the substrate SUB having the anode electrode ANO, a bank BN is formed over the area having the switching thin film transistor ST, the driving thin film transistor DT and the various lines DL, SL and VDD, for defining the light emitting area. The exposed portion of the anode electrode ANO by the bank BN would be the light emitting area. On the anode electrode ANO exposed from the bank BN, the organic light emitting layer OL is formed. On the organic light emitting layer OL, the cathode electrode ACT is formed.
On the substrate SUB having the cathode electrode CAT, a spacer SP is disposed. The spacer SP is preferably formed on the bank BN, the non-aperture area. An encap substrate (or encapsulation substrate) ENC is joined with the lower substrate SUB with the spacer SP there-between. In order to join the encap substrate ENC and the lower substrate SUB, an adhesive layer or adhesive material may be further included between the encap substrate ENC and the lower substrate SUB.
For the case of the bottom emission type and full color organic light emitting diode display, the lights from the organic light emitting layer OL go out to the lower substrate SUB. Therefore, between the overcoat layer OC and the passivation layer PAS, a color filter CF may be further included, and the anode electrode ANO would be made of transparent conductive material. Further, it is preferable that the cathode electrode CAT includes metal material having high reflective property so that the lights from the organic light emitting layer OL can be reflected downward effectively. The organic light emitting layer OL may include an organic material generating white lights. The organic light emitting layer OL and the cathode electrode CAT may be disposed over the whole surface of the substrate SUB.
Hereinafter, referring to FIG. 5, the top emission type organic light emitting diode display for representing full color according to the related art will be explained. The basic structure of the top emission type is very similar with the bottom emission type. Therefore, the same explanation will not be duplicated. For the top emission type, the lights generated from the organic light emitting layer OL will go up to the encap substrate ENC attached on the lower substrate SUB. Therefore, it is preferable that the anode electrode ANO is made of a reflective metal material and the cathode electrode CAT is made of a transparent conductive material.
To represent/reproduce the full color, the organic light emitting layer OL may include an organic material which can emits any one color of red, green and blue. Otherwise, the organic light emitting layer OL may include an organic material which can emits the white color. In that case, the color filters CF may be disposed on the organic light emitting layer OL or cathode electrode CAT. Here, in convenience, the case where the color filter CF is disposed on the cathode electrode CAT is explained. The color filters CF may be disposed in a matrix manner in which a color filter set of red R, green G and blue B is alternatively arrayed.
For the bottom emission type, the user observes the display at the lower substrate SUB. On the contrary, for the top emission type, the user observes the display at the encap substrate ENC. Therefore, the ambient lights may be reflected by the outer surface of the lower substrate SUB or the encap substrate ENC, so that these reflected lights may hinder the seeing quality of the observer. Specially, in the case that the black matrix is disposed between each pixel areas, the ambient lights may be reflected by the black matrix.
To prevent the degradation of display quality be the reflected ambient lights, a polarization plate of λ/4 retardation may be attached on the surface seen by the observer. For example of the bottom emission type, a polarization film POL may be attached on the outer surface of the lower substrate SUB. For another example of the top emission type, a polarization film POL may be attached on the outer surface of the encap substrate ENC. However, attaching the polarization film POL, the transmittance ratio of the whole lights is lowered, so that the display quality may be degraded also. Further, for compensating the lowered brightness, more power consumption may be required.
In addition, in order to manufacture the full color organic light emitting diode display, it is required that the organic light emitting layer can be formed individually for representing any one of red, green and blue colors corresponding to each pixel area. However, by the currently used photolithography technology, it is very hard to pattern the organic light emitting material individually corresponding to each pixel area. So, for forming organic light emitting layer corresponding to each pixel area, it is preferable that the individual pixel area of the organic light emitting layer is formed by evaporating method using the screen mask.
For the case of the organic light emitting diode display having a 15 inch or less size, the organic light emitting layer OL may be selectively formed on the anode electrode ANO. For example, by a manufacturing process using a screen mask, the organic light emitting layer can be deposited at some specific area. However, for a large area organic light emitting diode display 20 inch to 100 inch size, it is very hard to deposit the organic light emitting layer on some specific area using the screen mask. The large area screen mask has very heavy weight so that it is hard to keep in perfectly plane condition. Therefore, it is hard to keep the evaporating distribution density in even condition on a large area surface. Thus a new technology or method for manufacturing a large area organic light emitting diode display is required.